The invention pertains to current sensors and particularly to magnetoresistive (MR) current sensors. More particularly, it pertains to MR sensors having low offsets.
The present current sensor is a closed-loop, non-contact, fast-responding, wide-bandwidth, field nulling current sensor. This sensor reveals parameters equivalent to other closed-loop approaches such as the closed loop Hall effect current sensor in the related art. It is the use of the MR sensor having a set/reset and offset nulling loop leads to ultra low offsets and ultra low offset drifts over all conditions in current measurement. It also has very low offset drift over wide ranges of operating temperatures. Because of the ultra low offset, the sensor provides very accurate measurements of current. It has an auto-zero offset reduction circuit, which has a separate feedback path to remove offset and offset drift from the circuit. The magnetic signal and offset signals are driven to their respective nulls by independent feedback loops. The offset feedback loop is not used in Hall effect type current sensors. The transient noise and spikes caused by the set/reset circuit are greatly reduced with this new feedback scheme. The sensor has a frequency response from DC to over 150 kHz and has a response time of less than one microsecond.